Surface mounted, high pin count integrated circuit packages have been dominated by quad flat packs (QFP's) with various pin configurations, for example, leadless, J-leaded, and gull wing leaded. These packages have closely spaced leads for making electrical connections distributed along the four peripheral edges of the flat packages. These packages have become limited and grown prohibitively large because the pins or electrical leads are confined to the edges of the flat packages. To address this limitation, a new package, a ball grid array (BGA) is not so confined because the electrical contact points are distributed over the entire bottom surface of the packages. More contact points can be located with greater spacing than with the QFP's. These contacts are solder balls which facilitate flow soldering of the packages onto a printed circuit board. BGA's are popular alternatives to QFP's.
Sockets that accept BGA's are necessary for testing, burn-in, re-programming, and sometimes for production use where the integrated circuit may need replacing. Several such sockets have been developed by various manufacturers to satisfy this need. Most of these sockets are of a clam shell design, where a hinged top opens to allow package entry, and closing the top retains the package within the socket. The socket includes a bed of contacts spaced to match the BGA contacts and a top located spring or spring loaded surface is arranged to press the package onto the bed of contacts to ensure electrical connection for all the contacts. Some of the prior art BGA sockets align the IC contacts in holes in a printed circuit board. The contacts are arranged to extend through the holes to the other side of the printed circuit board where electrical connections are made. Such an arrangement of surrounding the contacts within holes and enclosing the BGA packages within the socket has the undesirable feature of retaining heat in the BGA packages during test or burn-in. In addition, this arrangement prevents heat sinks from being mounted onto the BGA package.
Such prior art sockets may be adequate for small scale handling of BGA packages, but, because of the many separate and complex physical actions needed to insert, test, and extract the BGA package, such clam shell sockets are: costly, unwieldy, and unreliable when used for production processing large numbers of BGA packages.
Another limitation of many available BGA sockets occurs since the socket contacts place forces onto the IC contacts in the same direction. These forces drive one side of the package against an abutment of the socket. The deflected socket contacts are opposed by the IC BGA contacts with the strength of the BGA package keeping the individual package contacts in their correct position. With a large number of contacts this cumulative force of many deflected contacts is very large and may physically damage the package.
It is an object of the present invention to provide a BGA socket needing few and simple physical operations to insert and extract an IC package. An additional object of this invention is to provide low resistance electrical contact to the package contacts by using uniquely shaped socket contacts that present sharp edges for high contact point interface pressure. A related object is to provide the package low resistance electrical contact during variations of socket temperature, shock, and vibration by using the socket contact shape for retention of the package's ball contacts. It is another object to provide short electrical current paths for the BGA package contacts through the socket contacts to the underlying printed circuit board.
Yet another object of the present invention is to provide a point of contact between the socket contact and the IC package ball contact that is above or near the BGA contact spherical ball equator and not in contact on the lower part of the ball such that the ball bottom surface is unaltered or deformed so that the BGA package will not be impaired for soldering to a printed circuit board or other such final end use.
It is another object of the present invention to provide a socket where there only substantial mechanical forces on the individual BGA ball contacts while no force is applied to the BGA package itself as a whole.
It is yet another object of the present invention to provide a BGA socket with no obstructions that need to be avoided when inserting and extracting the BGA package.
It is another object to provide a BGA socket that provides superior heat dissipation capabilities.